In the past, various methods have been known to insert component leads through mounting holes in printed circuit substrates and to fasten the leads to the substrate in preparation for a lead-attaching operation, such as wave soldering. Probably the most common method used in the past, particularly with flexible printed circuits involving thin substrates of a flexible plastic material, has involved inserting straight, oversized leads downward into holes formed in the substrate, cutting or swaging the leads to length while holding the component body down against the substrate to fasten the lead and component in preparation for the soldering operation.
One object of the invention is to provide improved lead configurations, assemblies and methods wherein the leads tips are so formed that, when the lead tips are inserted through the substrate mounting holes, the tips automatically fasten and lock the component to the substrate in the desired position, thus eliminating the clipping, swaging and hold-down steps employed in the type of prior-art operation described in the preceding paragraph.
In addition, we are aware of two prior patents, Hathorn U.S. Pat. No. 2,754,486 and Rausina U.S. Pat. No. 3,584,495, both herein incorporated by reference, that disclose certain prior-art techniques wherein the leads are preformed with an arcuate crimped end section (Hathorn) or an outwardly bowed compression-fit section (Rausina, FIG. 8) so as to physically engage portions of a substrate in the vicinity of a mounting hole in order to temporarily fasten the component leads mechanically to the substrate for a soldering operation.
Further objects of the invention are to provide improved lead-tip configurations and methods of assembly for automatic fastening of the leads to the substrates, wherein the lead tips are positively locked to the substrate so that the components may be pulled out or accidentally dislodged from the substrate during the time interval between component assembly and the soldering operation.
Another object is to provide lead configurations and methods, wherein the lead tips are cammed inward or outward by the walls of the mounting holes during lead insertion, so as to automatically correct for any misalignment of the leads with the corresponding mounting holes.
A further object is to provide improved structures and methods wherein portions of the lead tip engage portions of the under surface of the substrate after lead insertion, so as to facilitate a wave soldering process of bonding the tips to adjacent contact pad areas deposited on the under surface of the substrate.
Another object is to provide improved techniques for inserting leads into through holes of flexible printed circuits having thin, flexible plastic substrates, which will provide a positive lock of the lead tip to the substrate, without damaging the substrate in the vicinity of the hole particularly with circuits involving conductive through holes.